Method of making oil gas interchangeable with natural gas



Oct. 18, 1955 E. s. PETTYJOHN EI'AL 2,721,123

METHOD OF MAKING OIL GAS INTERCHANGEABLE WITH NATURAL GAS 3 Sheets-Sheet 1 Filed May 10, 1952 2772702? A2" /a/m 42223 72. ,2 726. 672 /z mM 7 1 M METHOD OF MAKING OIL. GAS INTERCHANGEABLE WITH NATURAL GAS 3 Sheets-Sheet 2 Filed May 10, 1952 i??? As.

Oct. 18, 1955 E. s. PETTYJOHN EIAL 2,721,123

METHOD OF MAKING OIL GAS INTERCHANGEABLE WITH NATURAL GAS Filed May 10, 1952 3 Sheets-Sheet 3 United States Patent h ETHQD OF lviAKlNG 61L GAS "INTERCHANGE- ABLE WITH NATURAL GAS Elmore S. Pettyjohn, Evanston, and Henry R. Linden,

Franldin Park, 111., assignors to Institute of Gas Tech- "noiogy, Chicago, 111., acorpcration of lllinois Application May 10, 1952, Serial No. 287,122

Claims. -(Cl.-48213) This invention relatesto'a'method of preparing a high heating 'value oil gas by cracking petroleum oils, particularly under conditions producing carbon deposits in amounts preventing continuous cracking due to the necessity for frequent removal of carbon deposits.

An important object of the invention is to provide a method of the nature indicated which can be carried out, if desired, in conventional regenerative apparatus "for making oil gas with only slight modification of such apparatus, and which is effective to make an oil gas more interchangeable with natural gas, .as compared with conventional regenerative methods for making :high heating value oil gas.

A specific object of the-present invention is to provide a method :of the nature indicated in which the-recovery of heating values of the material being cracked is particularly etficient.

Qther and further objects and features of the present invention will become apparent :from the following description and appended claims as illustrated by the accompanying drawings showing, diagrammaticallyand by way of examples, apparatus for carrying out the methods of the present invention. More particularly:

Fig. 1 is a vertical, longitudinal, sectional view (with parts shown in elevation) of a regenerative apparatus according to the present invention'for makinghigh heating value oil gas;

Fig. 2 is a fragmentary view of the main gas ductof the apparatus of 'Fig. 1 as modified in accordance with the disclosure in the copending'application of Elmore 'S. Pettyjohn entitled Oil Gas Plant, Serial No. 270,956, filed February 11, 1952.

Fig. 3 is a vertical, longitudinal, sectional view (with parts shown in elevation) of another regenerative apparatus according to the present invention for making high heating value-oil gas;

Fig. 4'is a fragmentary view of'the main gas duct of the apparatus of Fig. -3 as modified in accordance .with the disclosure in the above-noted copending application of Elmore 'S. Pettyjohn;

Fig. 5 is a vertical, longitudinal, sectional View :(with parts shown in elevation) of a non-regenerative apparatus according 'to the present invention for making high heating value oil gas; and

Fig. 6 is a fragmentary view of the main gas duct of the apparatus of Fig.Sasmodifiedin'accordance'with the disclosure in the above-noted copending application of Elmore S. Pettyjohn.

When proceeding according to the present invention, cracking of a normally liquid petroleum fraction is carried out in an atmosphere comprising low .molecular weight hydrocarbon gases and, if desired, also hydrogen. The hydrocarbon content of the said atmosphere should be at least 50% and preferably at least 75%. Examples of such an atmosphere are natural gas .or oil gas. The product gas thus obtained is almost completely interchangeable With natural gas and-can readily be rendered 2,721,123 Patented Oct. 18, 1955 completely and absolutely interchangeable with natural gas by catalytic autohydrogenation. Further, when the cracking atmosphere comprises or more methane, as when a liquid petroleum fraction is cracked in an atmosphereof natural gas, the recovery of heating value from the petroleum liquid is far greater than the recovery 'obtained when cracking according to conventional methods (in a steam atmosphere). Thus, a fuel gas absolutely interchangeable with natural gas can easily be prepared according to the present invention from normally liquid petroleum fractions with an exceptionally eificient recovery of the heating value of said liquid petroleum fractions.

Referring now to Fig. 1, the apparatus there shown includes two generators 10 and 12 disposed adjacently each other and two superheaters 14 and 16, disposed, -respectively, adjacently the generator 10 and the generator 12. At their bottoms, the generator 10 and the super- 'heater 14 are interconnected by a duct 18 to form a first generator-superheater pair, while the generator 12 and the superheater '16 are similarly interconnected by a conduit 20 to form a second generator-superheater:pair. The generators 10 and 12 and the superheaters 14 and 16 are provided with-interior checker brick work 22 made up of layers of closely spaced bricks arranged in closely overlapping position (as between the various layers) 'so as to provide a maximum number of tortuous gas passages whereby highly eflicient heat exchange is promoted between the gas and the brickwork. Due to the overlapping of-the checker'bricks, each 'brick structure forms a unifiedmass perforated by a large number of gas passages, with the result that the temperature therein will be substantially uniform. The cracking efiected withineach brick structure willtherefore be uniform throughout each brick work.

over duct 32. The roofs of the superheaters 14 and 16 are likewise arched abovethe brickwork therein and are each :formed, respectively, with central vertical apertures 34-and 36 receiving vertical ducts 38 and 40 having upper openings closed by valves 42 and 44.

Stacks 46 are provided above the upper ends of the ducts 38 and 40 to receive gases vented therefrom when the valves 42 and 44 are opened.

An 'air duct 48 having a valve 59 discharges into the duct 28 leading into the generator 18 andanother air *duct 52 having a valve 54 discharges air into the duct 30 leading into the generator 12. An oil spray device 56 for the generator '10 extends through the duct 28 and is supplied with oil .to :be cracked through a :pipe 58 having a valve 60 and with oil to be burned 'foriheating through a pipe 62 having a valve '64. An oil spray device 66 'forthc generator 12 extends through the-duct 30 and is supplied with oil to be :burned for heating through a pipe 68 having a valve 74 and with oil to be cracked through a pipe 72 having a valve 74.

A .gasduct 76 branches off from the duct 38 of :the superheater 14 and has connected thereto .an air duct 78 valved at :80 as well as a steam pipe *82 valved at 84. Similarly, a gas duct 86 branches off 'from the duct 40=of the superheater 16 and has connected thereto an air duct 88 valved at 90 as well as a steam pipe 92 valved at 94. Both ducts 76 and 86 discharge into a main gas duct 96 leading to a wash Ibox'98 containing liquid 100 into which the lower end of the :main gas in the second generator-superheater pair.

'into thesuperheater 14 and into the superheater 16. In

each case, the path of gas flow includes both generatorsuperheater pairs.

In the operation of the apparatus of Fig. 1 through a four-stage cycle, a first blast period is initiated by closing the valve 42, then opening the valve 44, and

. moving the valve 104 to close the outlet of. the duct 76.

Primary air is admitted through the conduit 78 by opening the valve 80. Secondary air is admitted through the conduit 52 by opening its valve 54 and oil for heating is supplied through thepipe 68 by opening its valve 70. The primary air passes through the superheater 14 and the generator wherein cracking has been effected in the preceding make stage, and the air then removes carbon deposited in the brick work of this first generatorsuperheater pair while being preheated before reaching the second generator-superheater pair. At the end of this blast period, the valves 54, 70, 80, and 44 are closed. The apparatus may be urged by briefly opening the valve 84 of the steam pipe 82 before the valve 44 is closed.

In the next succeeding make period, oil is cracked For this purpose, the valve 112 of the pipe 110 is opened to introduce natural gas or oil gas through a path including the first generator-superheater pair and the valve 74 of the pipe 72 is opened to supply oil to the generator 12. The make gas leaves the top of the superheater 16 and passes through the ducts 86 and 96, through the wash box 98 and into the gas main 102. During this period, carbon is deposited in the brick work of the second generatorsuperheater set. At the conclusion of this make period, the valves 74 and 112 are closed and the valve 104 is moved to close the outlet of the duct 86 into the duct 96 and to open the outlet of the duct 76.

In the next succeeding blast period, the valve 42 is opened and the valve 94 of the steam pipe 92 may then be opened briefly to purge the apparatus. Primary air is admitted through the pipe 88 by opening the valve 90 to remove the carbon deposits from the brick work in the generator 12 and superheater 16, the air being preheated while passing therethrough. Secondary air is admitted from the pipe 48 by opening its valve 50 and oil 'is supplied from the pipe 62 by opening the valve 64. At the end of the blast period, the valves 64, 90, 50, and 4-2 are closed. Before the valve 90 is closed, the

valve 94 of the steam pipe 92 may be opened briefly to purge'the apparatus.

In'the next-succeeding make period, the valve 116 of the pipe 114 is opened to introduce natural gas or oil gas through a path including the second generatorsuper heater pair and oil is supplied to the generator .10 by opening the valve 60 in the oil pipe 58. The make 'gas leaves the top of the superheater 14 and passes through the ducts 76 and 96, through the Wash box 98 and into the gas main 102. During this period, carbon is deposited in the brick work in the first generatorsuperheater pair. At the conclusion of this make period,

, valves 60 and 116 are closed and the valve 104 is moved to close the outlet of the duct 76 into the duct 96 and to open the outlet of the duct 86. The valve 94 is then opened, and the valve 84 of the steam pipe 82 may be opened briefly to purge the apparatus. The apparatus is then ready for a repetition of the four-stage cyclic regenerative process above describedl In the above-described process oil gas or natural gas are introduced in one superheater-generator pair while oil is introduced in the generator of the other pair so that the oil is cracked in an atmosphere of preheated and partially reformed natural gas or r'ecracked oil gas. As a. result, the make gas produced is more completely interchangeable with natural gas, and, in the case of using as a cracking atmosphere a gas with a high methane content, a higher conversion of oil to gas is secured.

By way of an example of the results obtainable when proceeding according to the present invention, a residual oil (22.2 A. P. I., 5.67 weight per cent Conradson car-' bon residue, and a C:H ratio of,-7.05) Was cracked in a pilot plant apparatus at 1550 F., a residence time of 4.3 seconds anda rate of methane flow of 32.6 cubic feet per gallon of oil. The resultsobtained are tabulated Attention is directed to the very efiicient heating value 7 recovery due to the effects of the high methane concentration in the cracking atmosphere evidenced by the tabulatedresults and to the fact that the gaseous mixture obtained is almost completely interchangeable with natural gas. For a complete discussion of the interchangeability of various fuel gases with natural gas, reference is made to our copending application entitled Fuel Gas Interchangeable with Natural Gas and Method of Preparing the Same.

Similar efficient heating recoveries can be obtained by cracking a normally liquid petroleum fraction in the indicated methane containing atmosphere at average temperatures ranging from about l350 to about 1700 F. and at residence times ranging from one up to ten but preferably only up to five seconds. The rate of methane flow is only limited by capacity of the apparatus and the available supply and composition of natural gas but would normally range from 10 to 50 cubic feet per gallon of oil being cracked.

By further way of examples, we tabulate herein below the conditions and results of a run with a representative heavy gas oil using a portion of the product gas instead of natural gas according to the present invention in a pilot plant similar to the above described apparatus.

Residence time, sec 2.68 Cracking temperature, F 1550 'Percent of oil gas recirculated 9.4 Total pressure in atmospheres 1.02 Make gas composition, vol. percent:

Carbon dioxide 0.7 Ethylene 21.2 Higher illuminants 3.6 Oxygen 0.3 Carbon monoxide 1.3 Hydrogen 22.5 Parafiins 50.2 Nitrogen 0.2 Heating value, B. t. u./s c. f-.* 1070 Specific gravity (air=l.000) 0.632 B. t. u. recovered in make gas/gallon of oil 81,700

. The above gas as blended with combustion gases to reduce its heating value, if required, is more interchangeable with natural gas than conventional high heating value oil gas, because of its higher paraffin content, lower illuminants content, lower heating value and lower specific gravity when compared to conventional high heating value oil gas produced at the same cracking temperature,

residence time and total pressure and using the same feed oil.

In general, the same type of oil gas can be produced by proceeding as follows. The cracking of the recirculated oil gas in the superheaters is carried out at an average temperature range from 1300 to 1600 F. and at a residence time of from 2 to seconds. One part of the recirculated oil gas may be cracked in the superheaters for each 2 to 10 parts of oil cracked in the generator.

The oil referred to hereinabove as being cracked in the generators includes the normally liquid fractions of natural gas and the petroleum oils including gasolines, naphtha, kerosene, fuel and gas oils, diesel oil, heavy gas oil and Bunker C oil. Ordinarily, heavy petroleum oils are employed. The cracking temperature ranges from 1300 to 1600 F., and the residence time from 1 to 5 seconds. The cracking temperature and residence time are maintained in the same manner as in the operation of a conventional regenerative apparatus for making (at atmospheric pressure) an oil gas having a diluent-free heating value of from 1000 to 1500 and preferably of from 1000 to 1200 B. t. u./s. c. f. It should be noted that in conventional operation it is generally not feasible to produce oil gases with diluent-free heating values below 1100 to 1200 B. t. u./s. c. f. when using the more economical residual oils since the required increase in severity of cracking efiected either by raising the cracking temperature or the residence time or both would result in the production of an exceedingly viscous and high free carbon content tar which is not readily handled in the plant and has a lower sales value.

Further, it should also be noted that in the operation (at atmospheric pressure) of a conventional regenerative apparatus for making oil gas having a heating value of from 700 to 1500 B. t. u./s. c. f. at a cracking temperature of from 1350 to 1700 F. and at a residence time of from 1 to 5 seconds, the composition of the gas formed efore dilution with combustion, blast or blow-run gases is fixed by the heating value thereof. However, at constant pressure and oil gas to steam ratio the diluent-free heating value of the gas is a function of the cracking temperature, residence time, oil properties and stream dilution. The above noted fixed relation between the gas composition and the heating value of the oil gas is tabulated as follows:

Diluent Free Heating Value of Gas in B. t. u./s. c. Gas Composition in Percent Paramns 48 Ethylene 25 Higher Illuminants. 4 6 8 Hydrogen 19 In proceeding according to the present invention, the cracking of the oil in the generators is carried out within the indicated ranges of temperature and residence time. Within these ranges, the conditions are adjusted to give a gas of the particular heating value desired, due regard being had for the fact that introduction in the superheaters of the indicated light hydrocarbons 1) reduces the heating value and the specific gravity of the diluentfree oil gas and thereby reduces the quantities of inert combustion gases which have to be added to obtain a heating value similar to that of natural gas, also (2) raises the paraflin content of the make gas and (3) reduces the make gas contents of olefins, all as compared with the make gas of the same final heating value obtained in the conventional regenerative apparatus for making oil gas at the same cracking temperatures and residence time.

Attention is directed to the fact that by proceeding according to the present invention it is possible to crack petroleum oils to produce an oil gas having properties such as composition, heating value and specific gravity more closely approaching those of natural gas without any increase in the severity of cracking, that is, in cracking temperature and/ or residence time. As a result the coil gas produced according to the present invention is such as to make the oil gas more completely interchangeable with natural gas than the oil gas produced by conventional cracking methods at equivalent severity of cracking because of the higher paraflin to olefin ratios in the product gases. For a complete discussion of the interchangeability of high heating value oil gas and natural gas, reference is made to our copending application entitled Fuel Gas Interchangeable With Natural Gas and Method of Making the Same, Serial No. 270,955, filed February 11, 1952.

A still higher parafiin to olefin and hydrogen ratio in the make gas (with consequently more complete interchangeability of the make gas with natural gas) can be secured by carrying out the make steps of the above process under superatmospheric pressure. For this purpose, the apparatns of Fig. 1 may be modified as illustrated in Fig. 2. As there shown, the duct 96 is constricted downstream of the valve 104, as indicated at 106. This constriction is dimensioned so as to dam up the oil gas pressure generated within the apparatus when oil is cracked therein. Further, the conduit 96 is made suificiently Wide downstream of the constriction 106 to permit expansion of oil gas passing therethrough whereby normal functioning of the wash box 58 is made possible. The modified apparatus of Fig. 2 is operated exactly as the apparatus of Fig. 1, but in the apparatus of Fig. 2 the cracking steps of the cycle are carried out under superatmospheric pressure (which is not true of the blasting steps), with resultant further improvement in the interchangeability of the make gas with natural gas, as noted hereinabove.

A regenerative apparatus of somewhat difierent design from that shown in Fig. 1 is illustrated in Fig. 3. The apparatus of the last-mentioned figure is generally U- shaped, having left and right shells indicated generally, respectively, at and 152 and interconnected at their bottoms by a conduit 154. The left shell 150 has provided therein spaced lower and upper checker brick Works 156 and 158 functioning similarly, respectively, to the generators and superheaters of the apparatus of Fig. 1. The right shell 152 is provided with similarly functioning spaced lower and upper checker brick works 160 and 162. An oil spray device 164 projecting into the interspace between the generator 156 and the superheater 158 is supplied with oil to be cracked through a pipe 166 valved at 168 and with oil to be burned for heating through a pipe 170 valved at 172. An air duct 174 valve at 176 also projects into the said interspace. Similarly, an oil spray device 178 projecting into the interspace between the generator 160 and the superheater 162 is supplied with oil to be cracked by a pipe 180 valved at 182 and with oil to be burned for heating through a pipe 184 valved at 186. An air duct 188 valved at 190 also projects into the interspace between the generator 160 and the superheater 162.

The roof of the shell 150 is arched above the brick Work 158 and is formed with a vertical aperture 192 receiving a vertical duct 194'- closed upwardly by a valve 196 which when opened permits venting of the shell 150 into a stack 198. Similarly, the shell 152 is arched above the brick 162 and is formed with a vertical aperture 200 receiving a vertical duct 202 closed upwardly by a valve 204 which when opened permits venting of the shell 152 into a stack 206. A gas duct 208 branches of from the duct 194 for the shell 150 and has an air duct 210 valved at 212 as well as a steam pipe 214 valved at 216 connected thereto. Similarly, a gas duct 220 branches 011 from the duct 202 for the shell 152 and has an air duct 222 valved at 224 as Well as a steam pipe 226 valved at 228 connected thereto. Both ducts 194 and 202 discharge into a gas duct 230 having a lower end dipping into liquid 232 in a wash box 234 from which make gas is discharged into a gas main 236. A valve 238 at the top of the gas duct 230 7 is movable between extreme positions closing the outlets into the gas duct 230, respectively, of the ducts 208 and 220.

As so far described, the'apparatus of Fig. 3 is conventional.

According to the present invention, a pipe 250 valved at 252 extends from the duct 220 into the duct 194 and another pipe 254 valved at 256 extends from the duct 208 into the duct 202. The pipes 250 and 254 serve to introduce,- respectively, into the superheaters 158 and 162, oil gas or natural gas.

In the operation of the apparatus of Fig. 3, blasting is first carried out. The valve 196 is closed, the valve 204 is opened, and the valve 238 is moved to close. the outlet of the duct 208. Primary air is admitted from the duct 210 by opening the valve 212 to remove any carbon deposits (formed in a preceding cracking or make period) in the superheater 158 and the generator 156, the primary air then being preheated on passage through these structures, Secondary air is admitted through the duct 188 by opening its valve 190, and oil for-burning is supplied by opening the valve 186 of the pipe 184. The, generator 160 and the superheater 162 are thus brought to cracking temperatures. At the end of the blast period, the valves 186, 190; 212, and 204 are closed. Before the valve 204 is closed, the apparatus may be purged by opening the steam valve 216 briefly.

In the next succeeding make period, the valve 182 of the oil pipe 180 is opened, as is also the valve 252 of the pipe 250. The make gas leaves the shell 152 through the duct 202 and passes through the ducts 220 and 230 and through the wash box 234 into the gas main 236. Carbon is deposited in the generator 160 and the superheater 162. At the end of the make period, the valves 182 and 252 are closed and the valve 238 is moved so as to close theoutlet of the duct 220.

:In the next succeeding blast period, the valve 196 is opened and the apparatus may then be purged by briefly opening the valve 228 of the steam pipe 226. Primary air is admitted from the duct 222 by opening the valve 224, to remove carbon deposited in the generator 160 and the superheater 162, this air being preheated on passing through the brick work of the structures. Secondary air is admitted from the conduit 174 by opening the valve 176 and oil is supplied to the spray device 164 from the pipe 170 by opening the valve 172. At the end of this blast period, the valves 172, 224, 176, and 196 are closed.

Before the valve 196 is closed, the apparatus may be purged by briefly opening the valve 228 of the steam pipe 226.

In the next succeeding make period, the valve 168 of the oil pipe 166 and the valve 256 of the pipe 254 are opened. The make gas leaves the top of the shell 150 and passes through the ducts 194, 208, and 230 and through the wash box 234 into the gas main 236. Carhon is deposited in the generator 156 and the superheater 158. At the conclusion of this make period, the valves 168 and 256 are closed, and the valve 238 is moved so as to close the outlet of the duct 208. The valve 204 is opened, and the apparatus may then be purged by briefly opening the valve 216 of the steam pipe 214, to make the apparatus ready for a repetition of the above-described four stage cyclic operation.

Apart from the stages hereinabove described, the apparatus of Fig. 3 is operated exactly as the apparatus of Fig. l to produce a make gas similar to that formed in the apparatus of Fig. 1.

By way of a modification of the apparatus of Fig. 3, the duct 230 may be constricted downstream of the valve 238, as shown at 240 in Fig. 4. This constriction is dimensioned so as to darn up the pressure of the oil gas generated in the. apparatus when oil is cracked therein. The pressure upstream of the constriction 240 does not interfere'with a normal operation of the wash box 234 for the gas issuing from the constriction expands downstream of the constriction before entering the wash box 234. The improved results obtained by cracking under pressure are discussed above in connection with the ,de-

scription of Fig. 2.

A non-generative oil gas set can also be employed to. practice the methods of the present invention. Such a set is shown in Figure 5 as including a generator 250 and a superheater 252 connected at their bottoms by a duct 254. The generator 250 and superheater 252 are both provided with layers of closely spaced oil cracking checker bricks 256 arranged in closely overlapping position (as between the various layers) so as to provide a maximum number of tortuous gas passages whereby highly eificient heat exchange between the gas and the brick work is promoted. Due to the overlapping of the generator bricks, the brick structure forms a unified mass perforated bya large number of gas passages, with the result that the temperature therein will be'substantially uniform. The cracking of the oil and of the oil gas will, therefore, be uniform throughout the brick work.

The roof of the generator 250 is arched above the brick work and formed with a central vertical aperture 258 through which discharges an air duct 260 provided with a valve 262. An oil pipe 264 having a valve 266 and terminating in a spray device extends through the air duct 260 and the aperture 258 into the generator 250 as does also pipe 268 for oil gas and/or natural gas having a valve 270. A steam pipe 272 valved at 274 discharges into the air duct 260 downstream of its valve 262.

The roof of the superheater 252 is arched above the brick work and is formed with a central vertical vent aperture 276 closed by a valve 278. A stack 280 is arranged above the valve 278 for removing gases discharged through the vent aperture 276. The arched roof of the superheater 252 is also formed with an aperture 282 receiving one end of a make gas exit duct 284 bent over elbow-Wise to provide a dependent terminal portion dipping into sealing liquid 286 in an enclosed wash box 288. A main gas duct 290 opens into the wash box 288 above the liquid level therein. The wash box 288 may be provided with a seal pot 292 and a drain pipe 294.

In the operation of the apparatus of Fig. 5, the generator 250 and superheater 252 are initially heated to cracking temperature (1350 to 1800" F., depending upon the oil to'be cracked and the rate of oil feeding into the generator). For thus purpose, the valve 278 is raised to open the vent 276, the valve 262 is opened to admit air through the duct 260 into the generator 250, the valve 266 in the oil pipe 264 is opened to spray oil into the generator, and the valve 272 in the steam pipe 274 is opened. The oil is burned in the generator 250, and the combustion gases flow downwardly through the generator 25% through the duct 254, upwardly through the superheater 252 and out through the vent aperture 276 into the stack 280. If any carbon is present in the generator 250 and superheater 252 (as by way of deposit formed in a preceding make step), this carbon is then burned oif. Such a heating and carbon removing stepor stage is carried out in' the manner conventional in connection with the operation of cyclic oil cracking apparatus of conventional construction.

After cracking temperatures have been reached in the generator 250 and superheater 252, the valve 262 in the air. duct 260 is closed. The valve 266 in the oil pipe 264 may then be closed for a short period or" time so that the steam issuing from the pipe 272 may purge the generator 250, the duct 254 and the superheater 252. Next, the valves 272 and 273 are closed, the valve 270 of the pipe 268 is opened and the valve 266 in the oil pipe 264 is again opened. Then the'oil sprayed into the generator 252 is cracked in an atmosphere of oil gas and/or natural gas, and the oil gasthus produced flows through the duct 254 into and through the superheater 252 Where further cracking of the oil gas takes place.

When the generator 250 and superheater 252 have cooled off in the course of the make period to a temperature at the lower end of the cracking temperature range, the valve 266 in the oil pipe 264 is closed and the oil gas remaining in the apparatus is purged by briefly opening the valve 274 of the steam line 272. After such purge, another blast is carried out, to raise the temperature of the brick work 256 and to remove therefrom carbon deposited during the make period.

The apparatus of Figure may be modified (according to the teaching of the said copending application of Elmore S. Pettyjohn, Serial No. 270,956) as shown in Figure 6, where the gas duct 284 is costricted as at 296, Cracking is carried out in the apparatus modified as shown in Figure 6 exactly as described hereinabove in connection with the operation of the apparatus of Figure 5. But due to the superatmospheric pressure prevailing during the cracking periods (which may range from 18 or 25 up to 100 more pounds per square inch, depending upon the size of the throat defined by the constriction 296 and the rate of oil gas generation), the make gas will contain a higher proportion of parafiins and lower proportions of hydrogen and of unsaturates (as compared with oil gas prepared at atmospheric pressure) and will, therefore, be more completely interchangeable (than the oil gas prepared at atmospheric pressure) and often absolutely interchangeable with natural gas.

The make gas obtained as described in the apparatus of Figures 1 to 6 can also be blended with an air-propane mixture to form a gas mixture that can be mixed with natural gas to meet peak load demands for natural gas. A greater amount of the propane-air mixture can be blended with the said make gas than with conventional oil gas without requiring readjustment of burners adjusted for burning natural gas.

The make gas obtained as described in the apparatus of Figures 1 to 6 can also be rendered absolutely interchangeable with natural gas. In this purpose, the gas is auto-hydrogenated by being passed over a hydrogenation catalyst under appropriate conditions. To secure such a gas absolutely interchangeable with natural gas, the catalyst temperature is maintained within the range of from 500 to 800 F. and the space velocity is maintained within the range of from 100 to 1000 cubic feet per cubic feet of catalyst volume per hour. The hydrogenation can conveniently be carried out at atmospheric pressure, but somewhat better conversions of ethylene are obtained at superatmospheric pressure. Any catalyst suitable for the hydrogenation of unsaturated hydrocarbons may be used, for instance, iron, nickel, cobalt, the oxides of these metals, platinum, palladium, vanadium and its oxide, and the oxides of chromium and molybdenum. By way of examples of such autohydrogenation, we have treated each of the above tabulated make gases (after removal of condensable vapors) by passing these gases over a catalyst consisting of nickel oxide precipitated on a kieselguhr carrier and containing about 10% elemental nickel in oxide form. The temperatures and space velocities amounted to about 541 and 151 in the case of the first make gas and to 754 F. and 141 in the case of the second make gas. In both instances, the parafiin contents of the gases were raised to above and the gases were rendered absolutely interchangeable with natural gas.

Many details of construction and procedure may be varied without departing from the principles of this invention, and it is therefore, not our intention to limit the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

We claim:

1. A method of making an oil gas which comprises thermally cracking a gas containing at least 50 per cent gaseous hydrocarbons, immediately passing the hot cracking products into a reactor, While simultaneously introducing into said reactor a normally liquid petroleum fraction to crack said fraction in the presence of said cracking products and in the absence of steam, said cracking being carried out at a temperature of 1350 F. to 1750 F., and at a residence time of 1 to 10 seconds.

2. A method of making an oil gas which comprises thermally cracking a gas containing at least per cent gaseous hydrocarbons, immediately passing the hot cracking products into a reactor, while simultaneously introducing into said reactor a normally liquid petroleum fraction to crack said fraction in the presence of said cracking products, and in the absence of steam, said cracking being carried out at a temperature of 1350 F. to 1750 F., and at a residence time of 1 to 5 seconds.

3. The method of claim 2 wherein the gaseous hydrocarbon is natural gas.

4. The method of claim 2 wherein the gaseous hydrocarbon is an oil gas.

5. A method of making an oil gas which comprises thermally cracking a gas containing at least 75 per cent gaseous hydrocarbons, immediately passing the hot cracking products into a reactor, while simultaneously introducing into said reactor a normally liquid petroleum fraction to crack said fraction in the presence of said cracking products, and in the absence of steam, the rate of flow of said gaseous hydrocarbon ranging from 10 to 50 cubic feet per gallon of petroleum liquid, said cracking being carried out at a temperature of 1350 F. to 1750 F., and at a residence time of 1 to 5 seconds.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,940 Nagel Jan. 19, 1937 2,192,815 Johnson et a1 Mar. 5, 1940 2,605,176 Pearson July 29, 1952 FOREIGN PATENTS 531,430 Germany Aug. 10, 1931 

1. A METHOD OF MAKING AN OIL GAS WHICH COMPRISES THERMALLY CRACKING A GAS CONTAINING AT LEAST 50 PER CENT GASEOUS HYDROCARBONS, IMMEDIATELY PASSING THE HOT CRACKING PRODUCTS INTO A REACTOR, WHILE SIMULTANEOUSLY INTRODUCING INTO SAID REACTOR A NORMALLY LIQUID PETROLEUM FRACTION TO CRACK SAID FRACTION IN THE PRESENCE OF SAID CRACKING PRODUCTS AND IN THE ABSENCE OF STEAM, SAID CRACKING BEING CARRIED OUT AT A TEMPERATURE OF 1350* F. TO 1750* F., AND AT A RESIDENCE TIME OF 1 TO 10 SECONDS. 